Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water potential to a region of lower water potential. Water potential is a measure of the tendency of water to move from one place to another. A partially permeable membrane is a membrane that allows some substances to pass through, but not others. In living cells, the cell membrane is partially permeable, and water can move in and out of the cell by osmosis.
What are the Factors Affecting Osmosis in Cells?
The main factors that affect osmosis in cells are the water potential gradient, the surface area of the membrane, the temperature, and the type of solute. The water potential gradient is the difference in water potential between the two regions separated by the membrane. The greater the water potential gradient, the faster the rate of osmosis. The surface area of the membrane is the area available for water molecules to cross. The larger the surface area, the faster the rate of osmosis. The temperature is the measure of the kinetic energy of the molecules. The higher the temperature, the faster the movement of the molecules, and the faster the rate of osmosis. The type of solute is the substance that is dissolved in the water. Some solutes can affect the water potential of the solution, and some can bind to the membrane and alter its permeability. The type of solute can affect the direction and the rate of osmosis.
What are the Different Types of Solutions and Their Effects on Cells?
Solutions can be classified into three types based on their water potential relative to the cell: isotonic, hypertonic and hypotonic. An isotonic solution has the same water potential as the cell. In an isotonic solution, there is no net movement of water across the membrane, and the cell remains the same size and shape. A hypertonic solution has a lower water potential than the cell. In a hypertonic solution, water moves out of the cell by osmosis, and the cell shrinks and becomes plasmolysed. A hypotonic solution has a higher water potential than the cell. In a hypotonic solution, water moves into the cell by osmosis, and the cell swells and becomes turgid. The effects of osmosis on plant and animal cells are different, because plant cells have a rigid cell wall that prevents them from bursting, while animal cells do not have a cell wall and can burst if the water intake is too high.
How to Test Osmosis in Potato and Sugar Solution?
One way to test osmosis in potato and sugar solution is to use potato cylinders as a model for cells, and measure the change in mass or length of the potato cylinders after soaking them in different concentrations of sugar solution. The following is a possible method to conduct the experiment:
- Cut six potato cylinders of equal size and mass using a cork borer and a scalpel. Record the initial mass and length of each potato cylinder.
- Prepare six beakers with 100 ml of sugar solution each, with concentrations of 0%, 2%, 4%, 6%, 8% and 10% sucrose. Label the beakers accordingly.
- Place one potato cylinder in each beaker, and leave them for 30 minutes.
- After 30 minutes, remove the potato cylinders from the beakers, and blot them dry with a paper towel. Record the final mass and length of each potato cylinder.
- Calculate the percentage change in mass and length of each potato cylinder using the formula: (final value – initial value) / initial value x 100%
- Plot a graph of percentage change in mass or length against sucrose concentration.
- Analyse the results and draw a conclusion.
Table 1: Concentration of Sugar Solution and Percentage Change in Mass and Length of Potato Cylinders
| Concentration of Sugar Solution (%) | Trial 1 (% change) | Trial 2 (% change) | Trial 3 (% change) | Average (% change) |
| 0 | ||||
| 2 | ||||
| 4 | ||||
| 6 | ||||
| 8 | ||||
| 10 |
Record the mass and length of each potato cylinder before and after immersing them in the sugar solution for 30 minutes.
What are the Safety, Ethical and Environmental Implications of the Experiment?
The safety implications of the experiment are the following:
- Wear gloves, goggles and a lab coat to protect the skin, eyes and clothing from the sugar solution and the sharp instruments.
- Use a cutting board and a scalpel holder to avoid injury when cutting the potato cylinders.
- Dispose of the potato cylinders and the sugar solution in a biohazard bin, and wash the beakers and the instruments thoroughly after the experiment.
The ethical implications of the experiment are the following:
- Use only the minimum amount of potato needed for the experiment, and avoid wasting the potato.
- Consider the source and the quality of the potato, and whether it is organic, genetically modified, or treated with pesticides or fertilizers.
- Consider the alternative methods or materials that could be used to test osmosis, such as artificial cells, dialysis tubing, or other plant tissues.
The environmental implications of the experiment are the following:
- Consider the carbon footprint and the water footprint of the potato production and transportation, and the energy and water consumption of the experiment.
- Consider the impact of the sugar production and transportation, and the potential pollution of the sugar solution if not disposed properly.
Practical Science 